Dzhokar Tsarnaev, one of the suspects in the marathon bombing, is still on the run. (Image: FBI)

Boston police today used Twitter and Facebook to reach out to residents during a manhunt for one of the men suspected of bombing the Boston Marathon this past Monday.

As of Friday morning, one of two main suspects in the marathon bombing is dead and the other is on the run. The manhunt has heavily armed police officers throughout the city, helicopters flying overhead, streets shut down and houses being searched.

Law enforcement officials needed to warn residents of Boston and nearby Watertown, Waltham, Newton and Cambridge to stay off the streets and to stay safely inside their homes. They alerted the media, but also turned to social networking sites Twitter and Facebook.

"There is an active incident ongoing in Watertown. Residents in that area are advised to remain in their homes. More details when available," tweeted @Boston_Police around 2:30 a.m. ET today.

Then two hours later, they tweeted, "#CommunityAlert: Residents of Watertown asked to stay indoors. Do not answer door unless instructed by a police officer."

The Boston Police Department also has been using Twitter to communicate with the media, telling them where they should set up and warning them not to compromise officer safety by broadcasting tactical positions of the homes being searched.

Twitter also was used this morning to tell residents that taxi service in the city was suspended and to ask residents to let them know if they see what could be the suspect's car.

"It's very smart. I think it's becoming crystal clear that the fastest way to reach the most people is through Twitter," said Zeus Kerravala, an analyst with ZK Research. "Personally, I found out about the bombings through Twitter."

He noted that a lot of people, of course, still get their information from television and radio news, but that's more limited than social media.

"TV and radio reach a set of people, but then it stops," Kerravala said. "Twitter reaches a number of people and then those people retweet the messages. Twitter announcements reach more than just the followers of the police department so the reach is multiplicative."

The Boston police also were using their Facebook page to put out multiple pictures of the suspects and to put out alerts about closings and warnings for people to stay inside.